- This is an application to test a novel hypotheses on the pathogenesis of RA; namely, that p53 mutations play a role in hyperplastic expansion of the synovium as a consequence of inflammation. Reactive oxygen species (ROS) and cytokines, present in the RA joint, are active apoptosis inducers, which should normally offset tissue expansion. The applicants propose that mutations in p53 can occur as a consequence of long-term exposure to the mutagenic action of ROS and cytokines, and further, that such mutations produce a state of resistance to apoptosis caused by ROS- and/or cytokine-induced DNA damage of synoviocytes. This resistance to apoptosis causes an accumulation of cells despite modest proliferation and this expansion results in pannus and joint damage. Thus, while RA may be predominantly an immunological disease, particularly at its inception, the applicants believe that nonimmunologic events (such as somatic defects in p53-mediated apoptotic response) make a major contribution to the progression of the disease. They plan to examine the role of p53 in apoptosis induced by ROS and cytokines in the relevant cell types (macrophages, fibroblasts-like synovial cells) and related cells. This will be done in culture, through the use of temperature-sensitive p53 mutants that permit conditional p53 function in a variety of cells. Since p53 is required in many cells for the induction of apoptosis following DNA damaging agents, the applicants expect that it will have such a role here as well. Concurrently, the applicants will examine RA joint tissues for the presence of p53 mutations. Then they will determine the influences of p53 mutation on synoviocyte function. Finally, they will assess the role of p53 in apoptosis and disease progression in mice lacking this gene through targeted disruption, in which they will induce joint inflammation by immunologic means. Together, these studies will form the basis for rigorous pursuit of this model, and if successful, it is their belief that the studies will have important consequences for our understanding of RA and provide new therapeutic strategies.